net.sf.saxon.expr

## Class SimpleExpression

- java.lang.Object
- - net.sf.saxon.expr.Expression
  - - net.sf.saxon.expr.SimpleExpression

- All Implemented Interfaces:
    Serializable, SourceLocator, LocationProvider, SaxonLocator, Callable, InstructionInfo, Locator

      public abstract class SimpleExpression
      extends Expression
      implements Callable

  An abstract implementation of Expression designed to make it easy to implement new expressions, in particular, expressions to support extension instructions.

  An implementation of this class must supply the `Callable.call(XPathContext, net.sf.saxon.om.Sequence[])` method to evaluate the expression and return its result.

  See Also:
    Serialized Form

- - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `protected Expression[]` | `arguments`
    `static Expression[]` | `NO_ARGUMENTS`

    - ### Fields inherited from class net.sf.saxon.expr.Expression

      `EFFECTIVE_BOOLEAN_VALUE, EVALUATE_METHOD, EVENT_FEED_METHOD, INHERITED_CONTEXT, INSPECTION_CONTEXT, ITEM_FEED_METHOD, ITERATE_METHOD, locationId, MAX_SEQUENCE_LENGTH, MAX_STRING_LENGTH, NAVIGATION_CONTEXT, NODE_VALUE_CONTEXT, PROCESS_METHOD, PUSH_SELECTION, staticProperties, UNBOUNDED_LOWER, UNBOUNDED_UPPER, W3C_CONSUMING, W3C_FREE_RANGING, W3C_GROUP_CONSUMING, W3C_MOTIONLESS, WATCH_METHOD`

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `SimpleExpression()` Constructor

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `int` | `computeCardinality()` Determine the static cardinality of the expression.
    `int` | `computeDependencies()` Compute the dependencies of an expression, as the union of the dependencies of its subexpressions.
    `Expression` | `copy()` Copy an expression.
    `Item` | `evaluateItem(XPathContext context)` Evaluate an expression as a single item.
    `void` | `explain(ExpressionPresenter destination)` Diagnostic print of expression structure.
    `Expression[]` | `getArguments()` Get the subexpressions (arguments to this expression)
    `String` | `getExpressionType()` Return a distinguishing name for the expression, for use in diagnostics.
    `ItemType` | `getItemType(TypeHierarchy th)` Determine the data type of the items returned by this expression.
    `SequenceIterator<? extends Item>` | `iterate(XPathContext context)` Return an Iterator to iterate over the values of a sequence.
    `Iterator<Expression>` | `iterateSubExpressions()` Get the immediate sub-expressions of this expression.
    `Expression` | `optimize(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType)` Perform optimisation of an expression and its subexpressions.
    `void` | `process(XPathContext context)` Process the instruction, without returning any tail calls
    `Expression` | `promote(PromotionOffer offer, Expression parent)` Offer promotion for this subexpression.
    `boolean` | `replaceSubExpression(Expression original, Expression replacement)` Replace one subexpression by a replacement subexpression
    `void` | `setArguments(Expression[] sub)` Set the immediate sub-expressions of this expression.
    `Expression` | `simplify(ExpressionVisitor visitor)` Simplify the expression
    `Expression` | `typeCheck(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType)` Perform type checking of an expression and its subexpressions.

    - ### Methods inherited from class net.sf.saxon.expr.Expression

      `addToPathMap, adoptChildExpression, checkForUpdatingSubexpressions, checkPermittedContents, computeSpecialProperties, computeStaticProperties, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, evaluatePendingUpdates, explain, getCardinality, getColumnNumber, getColumnNumber, getConstructType, getContainer, getDependencies, getEvaluationMethod, getExecutable, getExpressionCompiler, getExpressionName, getHostLanguage, getImplementationMethod, getIntegerBounds, getIntrinsicDependencies, getLineNumber, getLineNumber, getLocationId, getLocationProvider, getObjectName, getProperties, getProperty, getPublicId, getSlotsUsed, getSpecialProperties, getStreamability, getStreamingAdjunct, getSystemId, getSystemId, hasVariableBinding, implementsStaticTypeCheck, isSubtreeExpression, isUpdatingExpression, isVacuousExpression, iterateEvents, iterateSubExpressionInfo, markTailFunctionCalls, resetLocalStaticProperties, setContainer, setEvaluationMethod, setFiltered, setFlattened, setLocationId, staticTypeCheck, suppressValidation, toPattern, toStreamingPattern, toString, typeError`

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait`

    - ### Methods inherited from interface net.sf.saxon.expr.Callable

      `call`

- - ### Field Detail

    - #### NO_ARGUMENTS

          public static final Expression[] NO_ARGUMENTS

    - #### arguments

          protected Expression[] arguments

  - ### Constructor Detail

    - #### SimpleExpression

          public SimpleExpression()

      Constructor

  - ### Method Detail

    - #### setArguments

          public void setArguments(Expression[] sub)

      Set the immediate sub-expressions of this expression.
      Parameters:
        `sub` - an array containing the sub-expressions of this expression

    - #### iterateSubExpressions

          public Iterator<Expression> iterateSubExpressions()

      Get the immediate sub-expressions of this expression.
      Overrides:
        `iterateSubExpressions` in class `Expression`
      Returns:
        an array containing the sub-expressions of this expression

    - #### replaceSubExpression

          public boolean replaceSubExpression(Expression original,
                                     Expression replacement)

      Replace one subexpression by a replacement subexpression
      Overrides:
        `replaceSubExpression` in class `Expression`
      Parameters:
        `original` - the original subexpression
        `replacement` - the replacement subexpression
      Returns:
        true if the original subexpression is found

    - #### simplify

          public Expression simplify(ExpressionVisitor visitor)
                              throws XPathException

      Simplify the expression
      Overrides:
        `simplify` in class `Expression`
      Parameters:
        `visitor` - an expression visitor
      Returns:
        the simplified expression
      Throws:
        `XPathException` - if an error is discovered during expression rewriting

    - #### typeCheck

          public Expression typeCheck(ExpressionVisitor visitor,
                             ExpressionVisitor.ContextItemType contextItemType)
                               throws XPathException

      Description copied from class: `Expression`
      Perform type checking of an expression and its subexpressions. This is the second phase of static optimization.

      This checks statically that the operands of the expression have the correct type; if necessary it generates code to do run-time type checking or type conversion. A static type error is reported only if execution cannot possibly succeed, that is, if a run-time type error is inevitable. The call may return a modified form of the expression.

      This method is called after all references to functions and variables have been resolved to the declaration of the function or variable. However, the types of such functions and variables may not be accurately known if they have not been explicitly declared.

      If the implementation returns a value other than "this", then it is required to ensure that the location information in the returned expression have been set up correctly. It should not rely on the caller to do this, although for historical reasons many callers do so.

      Overrides:
        `typeCheck` in class `Expression`
      Parameters:
        `visitor` - an expression visitor
        `contextItemType` - the static type of "." at the point where this expression is invoked. The parameter is set to null if it is known statically that the context item will be undefined. If the type of the context item is not known statically, the argument is set to `Type.ITEM_TYPE`
      Returns:
        the original expression, rewritten to perform necessary run-time type checks, and to perform other type-related optimizations
      Throws:
        `XPathException` - if an error is discovered during this phase (typically a type error)

    - #### optimize

          public Expression optimize(ExpressionVisitor visitor,
                            ExpressionVisitor.ContextItemType contextItemType)
                              throws XPathException

      Description copied from class: `Expression`
      Perform optimisation of an expression and its subexpressions. This is the third and final phase of static optimization.

      This method is called after all references to functions and variables have been resolved to the declaration of the function or variable, and after all type checking has been done.

      Overrides:
        `optimize` in class `Expression`
      Parameters:
        `visitor` - an expression visitor
        `contextItemType` - the static type of "." at the point where this expression is invoked. The parameter is set to null if it is known statically that the context item will be undefined. If the type of the context item is not known statically, the argument is set to `Type.ITEM_TYPE`
      Returns:
        the original expression, rewritten if appropriate to optimize execution
      Throws:
        `XPathException` - if an error is discovered during this phase (typically a type error)

    - #### copy

          public Expression copy()

      Copy an expression. This makes a deep copy.
      Specified by:
        `copy` in class `Expression`
      Returns:
        the copy of the original expression

    - #### promote

          public Expression promote(PromotionOffer offer,
                           Expression parent)
                             throws XPathException

      Offer promotion for this subexpression. The offer will be accepted if the subexpression is not dependent on the factors (e.g. the context item) identified in the PromotionOffer. By default the offer is not accepted - this is appropriate in the case of simple expressions such as constant values and variable references where promotion would give no performance advantage. This method is always called at compile time.
      Overrides:
        `promote` in class `Expression`
      Parameters:
        `offer` - details of the offer, for example the offer to move expressions that don't depend on the context to an outer level in the containing expression
        `parent` - the parent of this expression
      Returns:
        if the offer is not accepted, return this expression unchanged. Otherwise return the result of rewriting the expression to promote this subexpression
      Throws:
        `XPathException` - if any error is detected

    - #### getItemType

          public ItemType getItemType(TypeHierarchy th)

      Determine the data type of the items returned by this expression. This implementation returns "item()", which can be overridden in a subclass.
      Specified by:
        `getItemType` in class `Expression`
      Parameters:
        `th` - the type hierarchy cache
      Returns:
        the data type

    - #### computeCardinality

          public int computeCardinality()

      Determine the static cardinality of the expression. This implementation returns "zero or more", which can be overridden in a subclass.
      Specified by:
        `computeCardinality` in class `Expression`
      Returns:
        the computed cardinality, as one of the values `StaticProperty.ALLOWS_ZERO_OR_ONE`, `StaticProperty.EXACTLY_ONE`, `StaticProperty.ALLOWS_ONE_OR_MORE`, `StaticProperty.ALLOWS_ZERO_OR_MORE`

    - #### computeDependencies

          public int computeDependencies()

      Compute the dependencies of an expression, as the union of the dependencies of its subexpressions. (This is overridden for path expressions and filter expressions, where the dependencies of a subexpression are not all propogated). This method should be called only once, to compute the dependencies; after that, getDependencies should be used.
      Overrides:
        `computeDependencies` in class `Expression`
      Returns:
        the depencies, as a bit-mask

    - #### evaluateItem

          public final Item evaluateItem(XPathContext context)
                                  throws XPathException

      Evaluate an expression as a single item. This always returns either a single Item or null (denoting the empty sequence). No conversion is done. This method should not be used unless the static type of the expression is a subtype of "item" or "item?": that is, it should not be called if the expression may return a sequence. There is no guarantee that this condition will be detected.
      Overrides:
        `evaluateItem` in class `Expression`
      Parameters:
        `context` - The context in which the expression is to be evaluated
      Returns:
        the node or atomic value that results from evaluating the expression; or null to indicate that the result is an empty sequence
      Throws:
        `XPathException` - if any dynamic error occurs evaluating the expression

    - #### iterate

          public final SequenceIterator<? extends Item> iterate(XPathContext context)
                                                         throws XPathException

      Return an Iterator to iterate over the values of a sequence. The value of every expression can be regarded as a sequence, so this method is supported for all expressions. This default implementation handles iteration for expressions that return singleton values: for non-singleton expressions, the subclass must provide its own implementation.
      Overrides:
        `iterate` in class `Expression`
      Parameters:
        `context` - supplies the context for evaluation
      Returns:
        a SequenceIterator that can be used to iterate over the result of the expression
      Throws:
        `XPathException` - if any dynamic error occurs evaluating the expression

    - #### process

          public final void process(XPathContext context)
                             throws XPathException

      Process the instruction, without returning any tail calls
      Overrides:
        `process` in class `Expression`
      Parameters:
        `context` - The dynamic context, giving access to the current node, the current variables, etc.
      Throws:
        `XPathException` - if a dynamic error occurs

    - #### getArguments

          public Expression[] getArguments()

      Get the subexpressions (arguments to this expression)
      Returns:
        the arguments, as an array

    - #### explain

          public void explain(ExpressionPresenter destination)

      Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.
      Specified by:
        `explain` in class `Expression`
      Parameters:
        `destination` - the expression presenter used to display the structure

    - #### getExpressionType

          public String getExpressionType()

      Return a distinguishing name for the expression, for use in diagnostics. By default the class name is used.
      Returns:
        a distinguishing name for the expression (defaults to the name of the implementation class)

Copyright (c) 2004-2013 Saxonica Limited. All rights reserved.